NASA / STScI

Mars looms large in a Hubble Space Telescope photo - and in the imaginations of those who have signed up for a one-way trip to the Red Planet. "It's not that I'm trying to get away," says 18-year-old Kayli McArthur, one of tens of thousands of applicants. "It's like I'm trying to strive for something more."

A one-way trip to Mars sounds like something you'd wish on your worst enemy — so why would more than 78,000 people from around the world pay up to $75 for a chance to die on another planet?

"I can say I have an ulterior motive," said David Brin, who has written more than a dozen science-fiction novels — including "The Postman," which was turned into a Kevin Costner movie in 1997. "I'd get a lot of writing done, and it might be memorable."

As a master of hard science fiction, the 62-year-old Brin knows better than most applicants what the first Red Planet settlers would face if they're sent off in 2022, as the Dutch-based Mars One venture has proposed.

The settlers would have to be sealed up in habitats, protected from harsh radiation, supplied with machine-made air and water, and nourished by whatever food can be grown on a cold, barren planet. They'd have to keep their sanity, millions of miles away from their families and Mission Control. Worst of all, they'd have to face the fact that there's no guarantee of ever going back.

Will this scheme actually work? "I give it a low probability of happening," Brin said, "and I don't consider it to be the most responsible thing I've ever seen."

Nevertheless, the venture has an attraction for Brin and tens of thousands of others, The ages of those listed in Mars One's database range from 18 to 71. All those applicants are facing a long road even before the first four-person crew gets off the planet. Mars One is accepting applicants through Aug. 31. The field of applicants would first be whittled down by panels of experts. Then they'd undergo trial by reality TV, followed by years of training.

"This may sound crazy, but it kind of reminds me of 'The Hunger Games,'" said Kayli McArthur, an 18-year-old student who's one of the youngest Mars One applicants. "It's cool that it would be televised, but that's not my whole thing."

On the other end of the age spectrum, 71-year-old psychiatrist Sanford Pomerantz is a little surprised that it's taking this long to get something like Mars One off the ground. "I thought by now we would have colonized Mars," said Pomerantz, who's currently the oldest applicant on Mars One's list.

So what's the appeal of Mars One? It's too early for Brin, McArthur and Pomerantz to give a lot of thought to their adventure on Mars, let alone their death on Mars. Instead, they're focusing on the adventure here on Earth. Here's what's behind their thinking:

Mars One

Click on the image to go to David Brin's Mars One application video.

David Brin: 'My main purpose is the conversation'
Brin sees Mars One as just one of a number of ventures aimed at expanding humanity's frontier, ranging from Virgin Galactic's suborbital space tours to Golden Spike's moon missions. "It's emblematic of the new era that we're about to enter at long last — what I call the barnstorming era," he said.

Like the daring airplane fliers of the 1920s, these 21st-century space barnstormers are willing to take bigger risks in hopes of providing bigger thrills — and eventually, earning bigger payoffs. The Mars One project is "a great way to get the discussion going," Brin said.

"You have to assume that it may not work, and that there will be a statue of you on Mars someday," he said. "I'm aware of the tradeoffs, and I'm willing to explore it further, but largely my main purpose is the conversation. We've got to be talking about how we can be a more exploratory people — a more interesting people, if you like."

Brin doesn't doubt that Mars One will find plenty of qualified (and interesting) people willing to take the risk.

"People who cannot imagine any sane person making that choice simply aren't envisioning the wide range of human diversity," said Brin, who has three children in school. "Consider what I told my family. By the very earliest date that Mars One might launch, I expect to be a spry 75-year-old whose kids are already successfully launched, and who might spend a few years doing something truly remarkable."

Even if it means dying on alien soil? Brin isn't completely sure he'd go that far, but he's willing to bet that others would.

"I think you'll find tens of thousands of people who, under those circumstances, will at least ponder it seriously," Brin said.

Mars One

Click on the image to go to Kayli McArthur's Mars One application video.

Kayli McArthur: 'I'm trying to strive for something more'
McArthur, a freshman at the University of Arizona, is one of more than three dozen 18-year-olds on Mars One's list of applicants. Ever since she applied, she's been hearing that she has her whole life ahead of her, so why would she want to leave it all behind for Mars?

"Being young doesn't make me want to do it any less because I have my whole life ahead of me," she said. "It makes it more exciting. ... I love all my friends, my guy friends, my family. It's not that I'm trying to get away. It's like I'm trying to strive for something more."

She has long dreamed of going into outer space, and she figures that her future degree in materials science would come in handy for creating the first interplanetary settlement. "Going to Mars, there are so many opportunities for that," she said. 

So far, her family hasn't stood in her way. "My family jokes, like, 'Oh, Kayli, have your fun with it,'" she said. If the selection process gets more serious, she suspects she might face more resistance from her parents. But not from her grandfather.

"My grandpa is a retired three-star [general] in the Air Force," she said. "We were talking about it. I get really worked up and excited, and he was talking about it, too, and being realistic about it. He said, 'That would be so cool if you were able to do it.' ... I know my grandpa would totally support me."

Mars One

Click on the image to go to Sanford Pomerantz's Mars One application video.

Sanford Pomerantz: 'Grandpa is going to Mars!'
Pomerantz is old enough to remember when the idea of sending people into outer space seemed as far out as the idea of sending people on a one-way trip to Mars seems now. One of the books that made an impression on him in grade school was Robert Heinlein's "Red Planet: A Colonial Boy on Mars," which was published in 1949.

"I started as a physics major in the university, but then I got accepted into med school and changed directions," he said. At the age of 71, he's still a practicing psychiatrist in Topeka, Kan. But he's also still holding onto that boyhood dream of spaceflight.

"The Mars thing is exciting, because I hope it'll stimulate people to get interested in space. ... And I hope it has the secondary effect of stimulating science education, especially in the U.S.," he said.

Just as McArthur believes that Mars will need a materials scientist, Pomerantz believes the crew will need a psychiatrist. "Psychologically, it's going to be an interesting challenge, but human beings are very adaptable," he said. "It'll be exciting to go to a whole new world. It'll be a major step in human evolution."

If Pomerantz ends up being selected for the first Mars crew, he's likely to become not only the oldest human to head for the Red Planet, but the oldest human to go on any space mission. (The current record-holder is John Glenn, who flew on the shuttle Discovery when he was 77 years old.) For now at least, that prospect doesn't faze Pomerantz's three children and two grandchildren. "The grandchildren are excited," he said. "It's like, 'Grandpa is going to Mars!'"

Pomerantz became a certified scuba diver just two years ago, and he still expects to be in good physical and mental shape for liftoff in 2022. "Remember, age is a state of mind," he said. "Chronologlcally, I may be 71. ... But psychologically and physically, I'm definitely in my 20s. I look in the mirror and say, 'Who's that old guy?'"

More about missions to Mars:

• Inspiration Mars: So crazy it just might work
• Buzz Aldrin envisions US leading way to Mars
• Cosmic Log archive on Mars

David Brin's latest science-fiction novel is "Existence," which is set in the latter part of the 21st century and involves matters way beyond Mars.

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the NBC News Science Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with NBCNews.com's stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

NASA / JPL-Caltech / Ken Kremer / Marco Di Lorenzo

A mosaic of images captured by NASA's Mars Curiosity rover on Sol 262 of its mission on Mars (May 2) shows its robotic arm in the foreground and Mount Sharp in the background. Two drill holes can be seen on the surface of the bedrock visible below the robotic arm's turret.

NASA's Curiosity rover is back at work in Yellowknife Bay, a rocky area inside Mars' Gale Crater — and if it takes good care of itself, it just might still be at work when humans hit the Red Planet.

At least that's the sentiment voiced by Michael Meyer, lead scientist for NASA's Mars Exploration Program, during this week's Humans to Mars Summit in Washington. "I anticipate the first astronaut we send can go and shake Curiosity's hand," he told Monday's audience at George Washington University. If that astronaut is able to come within hand-shaking distance, the gesture would serve as a thank-you for years of service by the nuclear-powered robot, Meyer said.

Last week, Curiosity resumed contact with controllers back at NASA's Jet Propulsion Laboratory after a weeks-long gap that was scheduled due to solar interference — and JPL has just finished upgrading the rover's software.

Images sent back on May 2 show the rover's robotic arm and its instrument-laden turret poised over Yellowknife Bay's bedrock. Scientist-writer Ken Kremer and his Italian colleague, Marco Di Lorenzo, assembled 13 images ("a Martian baker's dozen") into the sepia-toned panorama you see above.

"She's back and flexing!" Kremer wrote in an email. 

Within a week or so, the rover will be drilling into Martian bedrock to flesh out its scientific findings about the habitability of ancient Mars. Then it'll start heading toward Mount Sharp (a.k.a. Aeolis Mons), a 3-mile-high (5-kilometer-high) mountain in Gale Crater. Scientists are hoping that the layers of rock on that mountainside have recorded billions of years' worth of geological changes.

Because Curiosity is powered by a plutonium-fueled radioisotope thermoelectric generator, the rover could keep going for decades — assuming that there aren't any mechanical breakdowns, of course. That's what fuels Meyer's hope that there'll be a human-machine handshake someday.

More than 70 percent of Americans are confident that humans will go to Mars by 2033, according to a survey conducted in February by Phillips & Company for the Boeing Co. and Explore Mars, the nonprofit group sponsoring this week's summit. But one of the summit's headliners, NASA Administrator Charlie Bolden, said that sending astronauts to Mars can't be done without technological innovation and financial support.

"I don’t know about you, but I’m not ready," The Washington Post quoted Bolden as saying. "I don’t have the capability to do it. NASA doesn’t have the capability to do that right now. But we’re on a path to be able to do it in the 2030s."

Will humans ever shake Curiosity's hand? When? Register your opinion in our unscientific survey above, and voice your views in the comment section below.

More about sending humans to Mars:

• Thousands want to take one-way trip to Mars
• Mars flyby in 2018? It's so crazy it just might work
• NBC News archive on Mars

You can follow the Humans to Mars Summit via streaming video. Check out Explore Mars' channel on Livestream for on-demand videos from Monday's sessions, plus live coverage of Tuesday's sessions.

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the NBC News Science Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with NBCNews.com's stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

NASA / JPL-Caltech

A Martian view from one of Curiosity's hazard avoidance cameras, transmitted back to Earth on Thursday, shows the shadow of the instrument turret on the rover's robotic arm.

NASA's Curiosity rover is back in business after a weeks-long communication gap caused by solar interference. The proof comes in the form of pictures transmitted back to Earth on Thursday from the 1-ton machine's vantage point at Yellowknife Bay on Mars.

"Can you hear me now? Conjunction is over. I have a clear view of Earth & am back to work!" the rover tweeted (with a little help from her entourage at NASA's Jet Propulsion Laboratory).

Dozens of raw images are on display on NASA's Mars Curiosity website, featuring rocky terrain in the foreground and the 3-mile-high (5-kilometer-high) peak known as Mount Sharp or Aeolis Mons in the background. Other Mars probes, including the Opportunity rover, Mars Odyssey and Mars Reconnaissance Orbiter, are back at work as well.

NASA's Red Planet probes were on hiatus for most of April due to an unfavorable alignment of Mars, Earth and the sun. During solar conjunction, the sun gets in the way of the communication lines between the two planets, and mission controllers generally put science operations on hold. Such conjunctions occur every 26 months. Opportunity has gone through several communication breaks during its nine years on Mars, but this is the first one to occur since Curiosity landed last August.

The spacecraft weren't completely idle during the break: Curiosity conducted in-place investigations and sent back limited transmissions via X-band radio to let controllers at NASA's Jet Propulsion Laboratory know that it was doing OK. Opportunity autonomously flipped its computer into safe mode during the break, apparently due to a glitch involving a routine camera check. A fresh set of software commands fixed the glitch, and on Wednesday controllers reported that Opportunity was back in working order.

Curiosity is due for its own software upgrade, and then the rover is scheduled to drill out a second sample of ground-up rock for analysis. The first sample, analyzed in March, suggested that the Yellowknife Bay environment was potentially habitable billions of years ago. Scientists want to use the follow-up sample to confirm what they saw in previous chemical analyses.

After Curiosity finishes up its work in Yellowknife Bay and its surroundings in the Glenelg area of Gale Crater, controllers plan to point the rover toward Mount Sharp, 6 miles (10 kilometers) away. The science team suspects that the mountain's many layers of rock will hold further evidence of ancient organic chemistry.

More about Mars:

• Cosmic Log archive on Curiosity
• Old phallic picture on Mars sparks new titters
• NASA lets poets send haiku to Red Planet

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

NASA / GSFC

The MAVEN orbiter, shown in this artist's conception, is to be launched toward Mars in November. NASA is taking names that will be digitized for inclusion on the spacecraft.

Poets, take note: NASA is looking for a few good haiku to send to the Red Planet aboard its MAVEN orbiter this fall.

If you're not the literary sort, don't worry: You can still submit your name to be included on a DVD that will be attached to the spacecraft. MAVEN is scheduled for launch from Cape Canaveral in Florida sometime after Nov. 18. In 2014, it'll go into Martian orbit to study changes in the planet's atmosphere over the course of at least one Earth year. Mission cost is $670 million. MAVEN is short for Mars Atmosphere and Volatile EvolutioN.

Send-a-name opportunities come around at least once every year or so, and they tend to be quite popular with the general public. More than 1.2 million names were collected for the Mars Science Laboratory mission: Those names were etched onto two microchips, each the size of a dime, and then the chips were placed in a protected corner of the Curiosity rover.

This time around, you can submit names via the MAVEN mission's "Going to Mars" website. All the names will be digitized and encoded onto a DVD that will be put on the spacecraft. You can also submit a personal message in the form of a haiku — a traditional form of three-line Japanese verse that has five syllables for the first line, seven syllables for the second line, and five syllables for the third line.

The deadline for submissions is July 1. An online public vote will be conducted beginning July 15 to select the top three haiku poems. Those three poems will be included on the spacecraft as well, and will be prominently displayed on the MAVEN website. Check the "Going to Mars" instructions to get the details and to register your name and message.

"The Going to Mars campaign offers people worldwide a way to make a personal connection to space, space exploration, and science in general, and share in our excitement about the MAVEN mission," Stephanie Renfrow, lead for the MAVEN Education and Public Outreach program at the University of Colorado's Laboratory for Atmospheric and Space Physics, said in a NASA news release announcing the campaign. To put it another way:

Space exploration
blends science and poetry,
blends heaven and earth. 

More about future space missions:

• MAVEN mission prepped for launch
• NASA plans 2020 Mars rover remake
• 13 new space missions for 2013

Alan Boyle is NBCNews.com's science editor (and was editor of his college's literary magazine more than three decades ago). Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

NASA / JPL / Cornell

When some people look at this nine-year-old picture from NASA's Spirit rover, they see a graphic depiction of manhood. Actually, it's standard operating procedure for making a turn on Mars.

Some Mars maniacs just won't grow up: A picture of the track patterns left behind by the Mars rovers' standard turning maneuver has drawn giggles and gasps — merely because it looks like a penis scrawled on the Red Planet.

"The rude drawing has emerged in a series of images taken by one of its rover machines. ... The latest pictures beamed back from one of the rovers show signs that the project's controllers have started to get a bit bored," The Sun, a British tabloid, reported on Wednesday.

Even Sarcastic Rover, one of Twitter's top parody personas, got into the act: "Since everyone's asking, let me just say that some other robot did this ... definitely not me," it tweeted.

The jibes from Sarcastic Rover and The Sun, and tons more like them, were sparked by a Reddit forum's discovery of the picture the day before. But this picture isn't the product of a bored (or filthy-minded) rover driver, and it wasn't beamed down recently. It's part of a classic nine-year-old panorama from NASA's Spirit rover, looking back toward its landing platform. (You can actually see the platform in the high-resolution version of the panorama.)

This type of rover wheel-track pattern, which could euphemistically be called "a bat and two balls," has been left on Mars many times, not only by Spirit (which gave up the ghost in 2010 or so), but also by Opportunity (which is still going strong more than nine years after landing on Mars) and Curiosity (which landed last year).

All those rovers have six wheels, three on each side, and they leave behind two parallel tracks when they're traveling in a straight line. When the rover has to make a turn, the wheels rotate in place to put the robot in the desired direction for the next leg of its trek. If the turn is significant enough, you get a nice set of circles at the end of a pair of parallel tracks.

Got it? Now we can move on — for instance, to lewd pictures from the Hubble Space Telescope.

NASA / ESA / STScI / AURA / La Plata Obs.

A sub-cloud of dust in the Carina Nebula displays what some have called "the cosmic finger of friendship."

More tracks from the Red Planet:

• That's one small step ... on Mars?
• Curiosity leaves tracks in Morse code
• 3-D adds depth to tracks on Mars

Tip o' the Log to Jia-Rui Cook at NASA's Jet Propulsion Laboratory for finding the original Spirit panorama from Mars.

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

Organizers of the Dutch-based Mars One project opened up their website on Monday to take applications for a one-way trip to Mars in 2022. 

That's right: These astronauts won't be coming back. The idea is to jump-start a permanent settlement on Mars, with more supplies and settlers arriving every couple of years.

The organizers say the $6 billion cost for the first landing would be covered through reality-TV deals and merchandising, but they skirted pointed questions about the plan's financial feasibility.

Mars One co-founder Bas Lansdorp compared the non-profit venture to the London Olympics, which reportedly brought in $3.8 billion in revenue for last summer's 17-day spectacle. "If you can make $1 billion per week just by having a large audience in the entire world, then suddenly $6 billion doesn't sound like so much anymore," he said.

He declined to provide a detailed breakdown of the costs during Monday's news conference in New York, largely because he didn't want to give away any competitive information about the talks being conducted with potential suppliers. "It would be very stupid for us to give the prices that have been quoted per component," he told reporters.

He acknowledged that the mission's financial aspects posed the greatest challenge. However, he said the drama surrounding Mars One's plan to send four-person crews to Mars, with no promise of return, was "exactly the greatness that makes it possible to finance this."

"It's easier to finance a mission to Mars than to finance a mission to the moon," he said.

Thousands register interest
There has certainly been lots of enthusiasm for the mission: Lansdorp said Mars One has received more than 10,000 emails from more than 100 countries around the world, voicing willingness to sign up for a one-way ticket to the Red Planet. Starting Monday, anyone 18 or older can formally apply — provided that they pay an application fee. Lansdorp said the fee ranges from $5 to $75, depending on the standard of living for the country of residence. U.S. residents, for example, will be charged $38.

Each applicant will have to submit a one-minute video explaining why he or she should be among the first humans on Mars. Applicants will be screened for physical and mental fitness, and will have to speak English. They should also be "mature and interesting," Mars One says. But chief medical director Norbert Kraft said there are no formal academic or professional prerequisites. "We will give the training," he said.

Mars One's business plan calls for the latter stages of the selection process to be broadcast on TV and the Internet. Twenty-four to 40 finalists would be chosen to go through years of training. At the end of the process, Mars One expects at least six crews to be ready for flight. Each crew would consist of two women and two men. Having six crews available would ensure against the possibility that someone gets sick — or gets "cold feet" — when it's time to fly to Mars, Kraft said.

The venture's time line calls for the first in a series of preparatory robotic missions to lift off in 2016. An exploratory rover would be sent to Mars in 2018, and another rover would head out in 2020 to get the chosen target site ready for human habitation. Eight robotic missions would be sent before the human crew sets out in 2022 on a seven-month cruise, Lansdorp said. The landing is currently scheduled for April 2023, "exactly 10 years from today," he said.

Organizers say the $6 billion raised through broadcast and marketing rights would cover costs through the first landing in 2023. Billions more would be required to keep the colony going and growing beyond that. 

Lansdorp said the project would be presented to international broadcasters at the Mipcom conference in Cannes, France, this October. He acknowledged that the time line might be delayed due to technical difficulties. "This will not be easy," he said. "There is lots of engineering and testing to be done before the first humans land." But he said the Mars One group is already in discussions with spaceflight companies including SpaceX and Paragon Space Development Corp. about the launch plans.

Grant Anderson, Paragon's senior vice president of operations, said his company was working on a concept design study that would be delivered to Mars One this summer. "The Mars One program is doing this right," Anderson said.

One of the potential scenarios would employ expanded SpaceX Dragon capsules for the missions, Lansdorp said. SpaceX's billionaire founder, Elon Musk, has repeatedly said it's technically possible to put humans on Mars in 10 years. There's already a "Red Dragon" plan for Mars landings, with an estimated price tag of $400 million or less per mission.

Reality check
Veteran rocket engineer Robert Zubrin, who is president of the non-profit Mars Society, agrees that Mars One's plan is technically feasible — but adds that it's incredibly challenging. "They have set a very high bar for themselves, and I'm not sure they have the resources," he told NBC News.

Former NASA mission planner Scott Hubbard, who is now a professor of aeronautics and astronautics at Stanford University, said landing on Mars safely ranked among the biggest challenges. "Anyone familiar with the 'seven minutes of terror' knows that getting anything substantial [to the Martian surface] is not a trivial issue," Hubbard said. Other challenges include weathering the radiation exposure and health effects of long-term weightlessness on the way to Mars; and truly being able to have astronauts live off the land once they get to Mars, with no possibility of heading back to Earth.

"It's certainly a bold concept, something that I don't know a government would ever contemplate," Hubbard said. He said the project could end up costing much more than the currently projected $6 billion.

The one-way nature of the Mars One trips didn't bother Zubrin: "There's nothing fantastical about that," he said. "We're all on a one-way trip to somewhere."

But Zubrin said another attention-getting trip, the Inspiration Mars plan to send a husband-and-wife crew on a flyby past the Red Planet in 2018, would be far less demanding. The price tag for that trip is thought to be on the order of $1 billion, and it already has the backing of millionaire space tourist Dennis Tito. A successful flyby in 2018 could conceivably generate interest in more ambitious missions, Zubrin said.

"If Inspiration Mars can do that, they will have significant credibility to raise large amounts of money to take humans to the Martian surface," Zubrin said.

When it comes to reality TV, money and the willingness to take on risks are the keys to success, said Hollywood producer David Krieff. He should know: Ten years ago, Krieff helped put pop singer Lance Bass through Russian cosmonaut training for a reality-TV project that would have sent him to the International Space Station. The project fizzled out when TV executives, potential sponsors and insurers got cold feet.

Krieff had some words of advice for Mars One's organizers: "I wish them luck, but I would say have the money in the bank — and most of all, have all the liabilities taken care of," he said. "The risks and the insurance and the money is a lot of work. These things are always more expensive than you expect."

More about missions to Mars:

• How to take a one-way trip to Mars
• Mars flyby in 2018? So crazy it might work
• NBC News archive on Mars

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

NASA / JPL-Caltech / MSSS

This graphic shows the relative sizes of Earth, Mars and Europa, an icy moon of Jupiter.

A British astrobiology conference has revived a years-old debate over the best place to look for life elsewhere in the solar system: Mars, or the moons of Jupiter and Saturn?

"For reasons I don't really understand, the wider solar system and the potential for life there has not been high priority," The Telegraph quoted Robert Pappalardo, a senior research scientist at NASA's Jet Propulsion Laboratory, as saying on BBC Radio 4.

Pappalardo's remarks were occasioned by this week's astrobiology conference at the UK Center for Astrobiology in Edinburgh, Scotland. The center recently established the International Subsurface Astrobiology Laboratory, or ISAL, half a mile (1 kilometer) beneath the surface in Yorkshire's Boulby mine. Biologists will use that facility to see how organisms hold up in extreme environments, learn about life's chemical signatures, and test instruments that could look for those signatures on other worlds.

Someday, one of the worlds may well be Europa, an icy moon of Jupiter. With a diameter of 1,945 miles (3,130 kilometers), Europa is just slightly smaller than Earth's moon, and yet it is thought to contain more water than Earth's oceans beneath a miles-deep layer of ice. Researchers recently suggested that hydrogen peroxide in the ice could serve as an energy supply for simple forms of life in the ocean hidden below.

Europa is the focus of Pappalardo's research, and for months he has been urging NASA to support a $2 billion mission to study Europa at close range. However, proposals for NASA missions to Europa have been losing out, in part because of the cost of missions to Mars. Last week's federal budget proposal for the next fiscal year provides no funding for a Europa mission, but it does fund Mars missions such as Maven (launching this year), InSight (launching in 2016) and a new science rover (launching in 2020).

Kevin Hand (JPL-Caltech) / Jack Cook (WHOI) / Howard Perlman (USGS)

If Europa's ocean is 100 kilometers (62 miles) deep, and all that water were gathered into a ball, it would have a radius of 877 kilometers (545 miles). This graphic compares that hypothetical ball of Europan water to the size of the Jovian moon itself, as well as all the water on planet Earth. Europa is thought to have two to three times the volume of water in Earth's oceans.

At February's annual meeting of the American Association for the Advancement of Science, Pappalardo worried that NASA's study of the outer solar system would go "radio-dark" in 2017, when the Cassini mission to Saturn and the Juno mission to Jupiter are both due to end. He continued that theme in this week's BBC interview.

"I worry that if Europa exploration is delayed, but then finally it happens some day, we might look back and say 'Why didn't we do that sooner?' Imagine 50 years from now, we get a lander there and find signs of life. All this time we'll have been looking in the wrong place," he was quoted as saying.

Europa isn't the only moon that intrigues astrobiologists: In the Jovian system, Callisto and Ganymede also have icy shells and may hold hidden oceans. Meanwhile, Cassini has repeatedly observed geysers of water ice rising from the surface of the Saturnian moon Enceladus — suggesting that liquid water and perhaps life may lie beneath the surface. Saturn's largest moon, Titan, has a thick atmosphere and seas of hydrocarbon that some scientists think could harbor a totally alien kind of life.

As for Mars, astrobiologists say hints of life could well lurk beneath the surface. To some extent, the Red Planet has been winning out over Europa and Enceladus because it's easier to get to. Moreover, NASA's vision calls for sending astronauts to Mars and its moons in the 2030s. NASA's robotic missions serve as precursors for those human voyages, as well as steps in a long-term program to learn about life in the universe.

Europa's fans can take heart in the fact that the European Space Agency is planning its own mission to Jupiter's moons: The Jupiter Icy Moons Explorer, or JUICE, is due for launch in 2022 and arrival at the Jovian system in 2030. There's also talk of a sample return mission that would target Enceladus' geysers, and a proposal to drop a boat onto Titan's seas.

So what if all of these worlds — Mars and Europa, Callisto and Ganymede, Titan and Enceladus — turn out to be lifeless? Charles Cockell, who heads the UK Center for Astrobiology, addressed that scenario in an interview with the BBC.

"A lot of people think astrobiology is some sort of hunt for life, and if we don't find life, it will be a big disappointment," Cockell said. "But in fact, that's not the case. The discovery of many lifeless planets across the universe, the discovery that the Earth might be unique as a place for life, would be an astonishing discovery in itself. It would be a very lonely discovery, but it would be an astonishing discovery."

More about the search for life:

• Which alien worlds are most livable?
• Maybe we are alone, after all 
• Cosmic Log archive on astrobiology

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

NASA

An artist's conception shows how Mars' atmosphere might have been stripped away by a stream of electrically charged particles from the sun.

Scientists say new readings from NASA's Curiosity rover have confirmed how Mars lost its once-thick atmosphere.

The measurements from Curiosity's Sample Analysis at Mars instrument, or SAM, provide fresh support for the view that a high-velocity stream of electrically charged particles from the sun has been stripping off Mars' atmosphere from the top. Mars is more vulnerable to that kind of atmospheric loss than Earth because it doesn't have a global magnetic field to serve as a shield against the solar wind.

Today, Mars' atmosphere is only 1 percent as dense as of Earth's on the surface, and consists mostly of carbon dioxide. The atmosphere is so thin that warmed-up ice turns directly into water vapor without passing through a liquid state. But scientists have seen geological evidence that water flowed abundantly over parts of the Red Planet billions of years ago. That implies that the atmospheric pressure was once much more Earthlike. So where did the missing air go?

Curiosity's science team presented the verdict from SAM on Monday during the European Geosciences Union's General Assembly in Vienna. The key clue is a precise measurement of various isotopes of argon, an inert gas that exists in trace amounts in the Martian atmosphere. Different isotopes of the same element have different atomic weights, and SAM was able to distinguish between those weights with unprecedented precision.

SAM's science team determined that the Martian atmosphere contains more of a lighter argon isotope (argon-36) than a heavier isotope (argon-38) — about four times as much. However, that ratio is lower than the solar system's original ratio of 5.5-to-1, as estimated from argon-isotope measurements of the sun and Jupiter. That would favor a process that stripped away Mars' ancient atmosphere from the top down, with more of the lighter isotopes of gases blown away.

Scientists have long suspected that the solar wind was the culprit for atmospheric loss, based on what happened to other isotopes in Martian air. But the argon measurements are more conclusive, because argon doesn't react with other elements. Thus, Curiosity's team could exclude a scenario in which constituents of the Martian atmosphere were removed by reacting with surface chemicals.

"We found arguably the clearest and most robust signature of atmospheric loss on Mars," Sushil Atreya, a SAM co-investigator at the University of Michigan at Ann Arbor, said in a NASA news release.

Slideshow: Curiosity's space odyssey to Mars

Trace the Curiosity rover's journey to Mars and see the pictures that the six-wheeled robot has sent back from the Red Planet.

Launch slideshow

More about Mars:

• Parachute flaps in the Martian breeze
• Probe to study Red Planet's atmosphere
• Rover finds organics, but are they from Mars?

For more about the SAM team's findings, check out this report from the BBC's Jonathan Amos.

 Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

DigitalSpace

An Orion exploration vehicle approaches a near-Earth asteroid in this artist's conception. Such a mission would be carried out in 2021 under the White House's new plan for NASA exploration beyond Earth orbit.

NASA's accelerated vision for exploration calls for moving a near-Earth asteroid even nearer to Earth, sending out astronauts to bring back samples within a decade, and then shifting the focus to Mars, a senior Obama administration official told NBC News on Saturday.

The official said the mission would "accomplish the president's challenge of sending humans to visit an asteroid by 2025 in a more cost-effective and potentially quicker time frame than under other scenarios." The official spoke on condition of anonymity because there was no authorization to discuss the plan publicly.

The source said more than $100 million would be sought for the mission and other asteroid-related activities in its budget request for the coming fiscal year, which is due to be sent to Congress on Wednesday. That confirms comments made on Friday by Sen. Bill Nelson, D-Fla., a one-time spaceflier who is now chairman of the Senate Commerce Subcommittee on Science and Space. It also confirms a report about the mission that appeared last month in Aviation Week.

The asteroid retrieval mission is based on a scenario set out last year by a study group at the Keck Institute for Space Studies. NASA's revised scenario would launch a robotic probe toward a 500-ton, 7- to 10-meter-wide (25- to 33-foot-wide) asteroid in 2017 or so. The probe would capture the space rock in a bag in 2019, and then pull it to a stable orbit in the vicinity of the moon, using a next-generation solar electric propulsion system. That would reduce the travel time for asteroid-bound astronauts from a matter of months to just a few days.

The Keck study estimated the total mission cost at $2.6 billion — but the administration official said the price tag could be reduced to $1 billion, or roughly $100 million a year, if the mission took advantage of an already-planned test flight for NASA's heavy-lift Space Launch System rocket and Orion crew exploration vehicle. That flight would send astronauts around the moon and back in 2021.

"This mission would combine the best of NASA's asteroid identification, technology development, and human exploration efforts to capture and redirect a small asteroid to just beyond the moon to set up a human mission using existing resources and equipment, including the heavy-lift rocket and deep-space capsule that have been under development for several years," the official said in an email.

The 2014 budget would set aside $78 million for planning the asteroid retrieval mission, plus $27 million to accelerate NASA's efforts to detect and characterize potentially hazardous asteroids. The federal government currently spends $20 million annually on asteroid detection.

Meteor sparked action
The official said the plan had been under discussion for months, but coalesced after February's meteor blast over Russia. The meteor's breakup injured more than 1,000 people and sparked a worldwide sensation. It also sparked a series of congressional hearings about threats from space, during which Republicans as well as Democrats hinted that they would support more funding to counter asteroid threats.

"This plan would help us prove we're smarter than the dinosaurs," said the official, referring to the asteroid that wiped out the dinosaurs and many other species 65 million years ago. An asteroid in the 7- to 10-meter range would be about half as wide as the one that broke up over Russia. That's far too small to pose any threat to Earth, even if the space rock was coming directly at our planet. But the captured asteroid could provide valuable insights for dealing with bigger ones in the future. 

Initial preparations for the mission won't have to wait for a deal to end budget sequestration, or approval of the budget for the 2014 fiscal year. NASA would begin immediately to identify the asteroid for retrieval, and take advantage of existing efforts funded by the agency's science, technology and human exploration directorates. The most expensive element of the plan, the multibillion-dollar Orion/SLS launch system, is already being funded under the terms of an agreement with Congress.

Discussions with NASA's international and commercial partners will continue in the months and years ahead, the official said. The retrieved asteroid could conceivably become a target for other scientific missions or asteroid-mining operations. In the process, governments might have to address issues surrounding the ownership and exploitation of space resources.

"We're trying to force the question," the official said. "We're trying to push the envelope on this new frontier."

Questions raised
Some observers have already raised questions about the plan, based on the advance reports. Scott Pace, the director of George Washington University's Space Policy Institute, told The Associated Press that it was a bad idea on scientific as well as diplomatic grounds. It would be better for the United States to join forces with other countries to conduct a comprehensive survey of all potentially dangerous asteroids, Pace said.

Rick Tumlinson, chairman of an asteroid-mining venture called Deep Space Industries, said he was concerned that NASA's asteroid mission might interfere with private-sector efforts — and he called on NASA to rely on private enterprise wherever possible. The administration official assured NBC News that cooperation with commercial ventures as well as other groups such as the B612 Foundation was part of the plan.

The official noted that the mission would provide a relatively low-cost route to satisfying President Barack Obama's goal of sending astronauts to a near-Earth asteroid by 2025. The lessons learned during the mission could be applied to future missions aimed at diverting other asteroids — perhaps to head off a potential threat, or conduct further scientific study, or exploit the potentially valuable resources that asteroids contain.

After the asteroid mission, NASA would turn its attention to a farther-out destination: Mars. The Obama administration has called for astronauts to travel to the Red Planet and its moons by the mid-2030s, and that would be the next major target for space exploration. The administration official told NBC News that other concepts, such as sending astronauts back to the moon or creating a deep-space platform beyond the far side of the moon, are not on the agenda for the foreseeable future. 

More about asteroids:

• Asteroid miners get boost from NASA
• Senator says asteroid mission is in the works
• Cosmic Log archive on asteroids

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

UW / MSNW

An artist's conception shows a spacecraft powered by a fusion-driven rocket. In this image, the crew would be in the forward chamber, shielded from the fusion reactor toward the back. Solar panels on the sides would collect energy to initiate the process that creates a fusion reaction.

Researchers at the University of Washington say they've built all the pieces for a fusion-powered rocket system that could get a crew to Mars in 30 days. Now they just have to put the pieces together and see if they work.

"If we can pull off a fusion demonstration in a year, with hundreds of thousands of dollars ... there might be a better, cheaper, faster path to using fusion in other applications," John Slough, a research assistant professor of aeronautics and astronautics, told NBC News.

Billions upon billions of dollars have been spent on fusion energy research over the past half-century — at places like the National Ignition Facility in California, where scientists are zapping deuterium-tritium pellets with lasers; Sandia National Laboratories in New Mexico, the home of the world's most powerful laboratory radiation source; and the ITER experimental facility in France, where the world's biggest magnetic plasma chamber is being built.

So far, none of those multibillion-dollar projects have hit break-even, let alone the fusion jackpot. Timetables for the advent of fusion energy applications have repeatedly shifted to the right, reviving the old joke that the dawn of the fusion age will always be 30 years away.

"The only answer to the 'always 30 years in the future' argument is that we simply demonstrate it," Slough said. And that's what he and his colleagues intend to do this summer, at their lab inside a converted warehouse in Redmond, Wash.

Harnessing fusion
It's obvious that nuclear fusion works: A prime example of the phenomenon can be seen every day, just 93 million miles away. Like other stars, our sun generates its power by combining lighter elements (like hydrogen) into heavier elements (like helium) under tremendous gravitational pressure. A tiny bit of mass from each nucleus is converted directly into energy, demonstrating the power of the equation E=mc².

Thermonuclear bombs operate on a similar principle. But it's not practical to set off bombs to produce peaceful energy, so how can the fusion reaction be controlled on a workable scale?

Slough and his colleagues are working on a system that shoots ringlets of metal into a specially designed magnetic field. The ringlets collapse around a tiny droplet of deuterium, a hydrogen isotope, compressing it so tightly that it produces a fusion reaction for a few millionths of a second. The reaction should result in a significant energy gain.

"It has gain, that's why we're doing it," Slough said. "It's just that the form the energy takes at the end is hot, magnetized metal plasma. ... The problem in the past was, what would you use it for? Because it kinda blows up."

That's where the magnetic field plays another role: In addition to compressing the metal rings around the deuterium target, the field would channel the spray of plasma out the back of the chamber, at a speed of up to 67,000 mph (30,000 meters per second). If a rocket ship could do that often enough — say, at least once a minute — Slough says you could send a human mission to Mars in one to three months, rather than the eight months it took to send NASA's Curiosity rover.

UW / MSNW

UW's Plasma Dynamics Lab has a vacuum chamber that is surrounded by two large, high-strength aluminum magnets. These magnets are powered by energy-storage capacitors that are connected by cables. The chamber is used to test a fusion-driven rocket technology.

Next steps
Slough's work at the University of Washington and a private-sector spin-off called MSNW has been supported by grants from the Department of Energy and NASA — including $600,000 from the NASA Innovative Advanced Concept Program, or NIAC. So far, researchers have created the deuterium droplets and heated them up to fusion temperatures. They've also tested the magnetic system for crushing ringlets of aluminum. "Now we've got to do them both together and see that work," Slough said.

The key experiments are due to take place starting in late summer, at the UW's Plasma Dynamics Lab in Redmond. If everything works, that would give the researchers the confidence to scale up the laboratory apparatus. For example, they'd use lithium rings instead of aluminum rings to increase the efficiency of the reaction.

Even if Slough is successful, it's not clear how long it would take to turn the technology into a viable rocket system. Other plasma-based propulsion systems — such as the Variable Specific Impulse Magnetoplasma Rocket, or VASIMR — have gone much further down the road of technology development. And some rocket scientists, such as the Mars Society's Robert Zubrin, think the whole idea of plasma propulsion is a potentially costly "hoax."

Despite all that, Slough's work could help kill another old joke about fusion: that it's the power source of the future — and always will be. What do you think? Please feel free to weigh in with your comments below.

More about fusion:

• Fast ride into space is in the works
• What's new on the fusion front?
• Levitating magnet coaxes fusion
• Cosmic Log archive on fusion

For more about the fusion research being conducted at the UW Plasma Dynamics Lab, check out this news release from the University of Washington, as well as YouTube animations showing how the propulsion system's magnetic nozzle and ring compression process would work.

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

NASA's Curiosity and Opportunity rovers aren't the only human-made objects that have been on the move on Mars: The Red Planet's winds have set Curiosity's discarded parachute rolling around on the surface, as seen in a series of images captured by the Mars Reconnaissance Orbiter over the course of five months.

The 65-foot-wide (20-meter-wide) parachute and the rover's protective backshell were thrown clear of the rover while it descended to its historic landing in Mars' Gale Crater last August. For a few weeks thereafter, they pretty much stayed where they were. But by the end of November, the orbiter's sharp-eyed HiRISE camera picked up changes in the parachute's shape and position. What's more, the dark marks left on the Martian surface by the backshell's impact started fading away.

The fading of the dark streaks could be explained by the deposition of airborne dust, according to the University of Arizona's Alfred McEwen, who heads the HiRISE science team. The winds that whip through Mars' thin atmosphere are also thought to be responsible for the parachute's changing position.

"This type of motion may kick off dust and keep parachutes on the surface bright, to help explain why the parachute from Viking 1 (landed in 1976) remains detectable," McEwen wrote in Wednesday's image advisory.

If you have red-blue glasses, check out this 3-D view of the parachute and the backshell.

NASA / JPL-Caltech / Univ. of Arizona

A color picture from the HiRISE camera on NASA's Mars Reconnaissance Orbiter shows the Curiosity rover's parachute and backshell spread out on the Martian surface.

Although the parachute may be on the move, Curiosity itself is definitely staying put for the rest of the month: Mars and Earth are on directly opposite sides of the sun, which interferes with radio communication. As a result, NASA will suspend sending commands to the rover starting on Thursday. Opportunity, MRO and the Mars Odyssey orbiter will be out of radio contact for most of April as well. Curiosity and Opportunity will be executing pre-programmed commands to continue their scientific work, and both rovers are expected to be back on the move in May.

More about Mars:

• Curiosity resumes rock analysis after glitch
• How a Martian mountain would look on Earth
• NBC News archive on Mars

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

NASA / JPL-Caltech / Marco Di Lorenzo / Ken Kremer

The Curiosity rover's instrument-laden robotic arm is front and center in this mosaic view captured by the Mars rover's NavCam system and assembled by Marco Di Lorenzo and Ken Kremer. The colorized black-and-white imagery was captured on March 23. Click on the image to see the full panorama.

After a week of down time due to a computer glitch, NASA's Mars Curiosity rover is once again sending back pictures of its rocky Red Planet locale at Yellowknife Bay. In this fresh panorama, the rover looks as if it's sticking its drill-equipped robotic arm right in your face.

"That drill is hungry, looking for something tasty to eat, and 'you' (loaded with water and organics) are it," jokes scientist-writer Ken Kremer, who collaborated with Italian colleague Marco Di Lorenzo to assemble the panorama.

Curiosity's percussive drill played a key role in the science team's most recently reported breakthrough: the finding that powder drilled out of a Martian rock contained the chemical traces of a life-friendly environment that existed on Mars billions of years ago. The team's chemical analysis of the powder indicated that the minerals were probably formed in the presence of drinkable water.

That kind of water no longer exists in liquid form on the Martian surface. The place where Curiosity is currently working may have once been in the vicinity of a riverbed, but it's now a cold and dry wasteland of sand and rock. In the weeks to come, Curiosity's scientists plan to drill into the rock again, looking for confirmatory clues about the potentially habitable environment in the Red Planet's past.

The plan has been held up due to a series of minor setbacks — including a memory failure that may have been due to a cosmic-ray strike, a precautionary stand-down to weather a solar storm, and most recently a computer file glitch that put the rover into safe mode. The Curiosity team has been carefully bringing the rover back to full operation, and this picture is presumably part of the checkout process.

It won't be long before the rover will once more have to reduce its contact with its handlers back on Earth, due to an Earth-Mars-sun conjunction that will interfere with radio signaling. Curiosity's communication gap is expected to last from April 4 to May 1, as detailed in a mission update from NASA's Jet Propulsion Laboratory. During the break, Curiosity is expected to carry on with its experiments, but the transmission of science data and images will have to wait until May. So let's enjoy these fresh images while we can.

For more of Curiosity's raw imagery, check out the galleries on JPL's Mars Science Laboratory website. You'll also find great pictures on UnmannedSpaceflight.com, where Kremer, Di Lorenzo and other image-processing gurus post their work. If you have 3-D glasses, whip 'em out and take a look at Ed Truthan's red-blue view of Curiosity's first drilling site.

Slideshow: Curiosity's space odyssey to Mars

Trace the Curiosity rover's journey to Mars and see the pictures that the six-wheeled robot has sent back from the Red Planet.

Launch slideshow

More about Mars:

• How a Martian mountain would look on Earth
• What's next for the Curiosity rover
• NBC News archive on Mars

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log and the rest of NBCNews.com's science and space coverage, sign up for the Tech & Science newsletter, delivered to your email in-box. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.